An Electron Microscope Must Use Electromagnet "Lenses" Shaped Like Donuts

question 69

Multiple Choice

An electron microscope must use electromagnet "lenses" shaped like donuts (with a hole in the middle) to direct the electrons onto the specimen. Why aren't they solid, like the lenses in a light microscope?

• A) A magnetic field cannot be applied across a completely solid object-there must be an opening within the object for the field to be applied through.
• B) Electrons are particles, and particles cannot travel through a solid item. The hole in the middle allows them to travel from the source of the electrons to the specimen.
• C) The electrons would destroy the electromagnet material unless there was a physical hole for them to travel through on their way to the specimen.
• D) The user has to be able to physically look through the magnets to focus the beam of electrons onto the specimen, since the metal of the magnets is opaque. Without a hole in the middle, the user wouldn't be able to see!
• E) All of the answer choices are correct.

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